Foundry composition and method



Patented June 6, 1950 FOUNDRY COMPOSITION AND METHOD Kenneth Ray Grube,Columbus, Ohio, assignor,

by mesne assignments, to Eastern Clay Products, Inc., Indiana, Pa., acorporation of Maryland No Drawing. Application April 7, 1948, SerialNo. 19,631

6 Claims. (Cl. 22-188) My application is a companion of my applicationSerial No. 768,941 of August 15, 1947, now Patent 2,491,006 of December13, 1949 entitled Method of conditioning foundry sand, and the presentinvention relates to foundry sands and molding compositions, and moreparticularly concerns the production of sands displaying good facingqualities, and of compositions for imparting the required good facingproperties to the sands. As well, it concerns the method of producingthe same.

An object of my invention is to provide facing I sands and moldcompositions wherein nearly all tendency of burning on of the sandparticles or the hinder, or both, to the poured metal is effectivelysuppressed; which sands and molding compositions are produced, insimple, ready and effective manner, and with thoroughly reliable,predictable and reproducible results, all with a minimum of investmentof both time, equipment and labor.

Another object is to provide a sand or mold composition of the generaltype described wherein the sand will fiow readily and can be molded andtamped into close conformity with the details of the pattern, whichpossesses a high degree of green strength together with requisitecontrollable and predictable developed or dry strength, and whichrequires but a small additive of binder to ensure requisite qualities ofmoldability.

Another object is to provide a method of treating foundry sands whereinthe added binder, while imparting its desired high binding qualities tothe mold composition to which it is admixed,

at the same time is effectively precluded from burning onto the pouredmetal and, as well, from fluxing the sand so that the latter can burnonto the poured'casting.

A further object is to provide a molding composition and a method ofproducing the same, wherein the controlled low developed or dry strengthwill permit thorough breakdown of the mold composition following openingof the flask, so that the used sand can be screened and the screenedproduct rehabilitated and readied for reuse by the admixture thereto ofbut a small quantity of my new treating composition.

All the foregoing, together with many additional highly desirableadvantages and objects, attend upon the practice of my invention, partof which will be obvious and part of which v.ill be pointed outhereinafter in greater detail during the course of the followingdescription.

As conductive to a more thorough understanding of my invention, it maybe noted at this time that the art of casting metals extends far backinto history. It has long been realized that for many reasons sand moldsare highly suited for the pouring of casting metals. This is in partattributable to the highly refractory nature of silica sands, and therelatively impervious qualities which they display to the hightemperatures of the poured metal.

A striking disadvantage is inherent in these sands, however, in thatthere is little, if any, quality of either cohesion of the grains of thesand amongst themselves or adherence thereof to the walls of the flask.A certain amount of cohesion is necessary between the particles of sandbefore they can display the qualities of moldability requisite inclosely conforming to and retaining the contours of the pattern. At thesame time, the sand must be reasonably free from tendency towardsadherence to the surface of the pattern. Such freedom from adherence canbe achieved in several manners, well recognized in the art, and notforming part of this invention.

Much eflort and research has been directed over the years to the problemof imparting the required satisfactory qualities of moldability to thesand. The admixture to the sand of binders has in large measure beendecided upon. Reliance upon the bonding qualities of suitable bindershas come more and more to the fore as the principal mode of resolvingthis problem. The binders are added directly to the sands. In recentyears the workers in the art have been directing their eiforts towardsthe montmorillonites, particularly southern bentonite, with itsnon-swelling colloidal qualities, and western bentonite, with itsswelling colloidal characteristics and its characteristic of impartinghigh dry strength.

Now, while this admixture of a binder is undesirable, diluting as itdoes, the good qualities of the sand, it constitutes a compromise whichis necessary in order to permit efiective use of the molding sand.lllustratively, it may be noted that the binder represents a source ofdecreased porosity. Its fine particles sifting into the intersticesbetween the particles of sand, particularly upon colloidal swelling whenwetted down, form a sort of solid solution or emulsion which tends toblock the venting of gases evolved when the metal is poured into themold. Blow holes sometimes result. Moreover, the clay serves as a flux,lowering the melting point of the sand and causing burning on of sand orclay or both, onto the poured metal when this latter is poured under 3the high temperature conditions which are necessary to liquefy certainmetals or alloys, illustratively, iron and steel.

Thus, much effort has been directed towards reducing the tendency of thebinder and sand.

towards burning onto the face of the poured casting. In this connectionit has been suggested to mix with the sand and binder some pitch or seacoal, or other hydrocarbon, the tendency of which is to form a reducingatmosphere in the region of the poured casting, thereby prevent ing theoxidizing of the surface of the. metal. Possibly, the vaporizedhydrocarbon serves as a physical insulation between the metal and thesilicous and argillaceous materials. Various disadvantages attend uponthe described practice, however, primarily because of the elements ofincreased expense, duration of processing and the tendency towardsdiminished porosity.

It has been suggested by a recent investigator that the tendency towardsburning on can be prevented in large measure by physically separatingthe bonding material from the particles of sand by some combustible,carbonaceous material. The theoryadvanced is that while upon pouring themetal undergoing casting, the temperature of this latter will fuse thebonding clay, nevertheless, the simultaneous combustion of thecarbonaceous material lying between the bond ing material and the samewill temporarily insulate these two, and will prevent the clay fromfiuxing the sand. By the time that the curtain of carbonaceous materialis entirely consumed, the poured metal will have passed into a solidphase, and it will be impossible for the clayfiuxed sand to burn on.Thus, in the prior art sand and carbonaceous material are mixedtogether, so that the sand is coated with the carbonaceous material,whereupon bentonite or other bonding clay of high degree of fineness isadded. The carbonaceous material which coats the sand physicallyseparates the sand and the bentonite, while the bentonite retains itsdesirable bonding qualities.

As distinguished from the prior art, my experiments disclosed that novelaction of the bentonite, entirely different from what had hitherto beenconceived to be its role in foundry compositions, could be availed of bydirectly mixing the hydrocarbon which produces the reducing atmosphereduring pouring with the binder, either just prior to or at the time thatthe sand is mixed therewith. In short,'by so doing, the hydrocarbonapparently efiectively encapsulates the binder, and prevents it fromfluxing the sand. Since a much smaller quantity of binder is employedthan sand, a much lesser quantity of hydrocarbon is required than whereattempt is made to encapsulate the particles of said. At the same timeeffective physical separation between the sand and binder is achieved.Even when the added ingredients are introduced into the mix at one time,then upon proper heating in the manner hereinafter discussed subsequentmicroscopic study demonstrated that the bentonite was thoroughlyencapsulated.

An important object of my invention, therefore, is to avoid insubstantial measure the several disadvantages and defects whichconfronted the art as the same heretofore existed; to provide a new modeof utilizing the bonding element thereof, wherein the particles ofbinder are thoroughly coated with a suitable non-thermal settingcarbonaceous material and substantially insulated from the foundry sand,which foundry composition involves the use of but limited quantities ofspecialized materials, is easily and rapidly produced in certain andpredictable manner, which displays high green strength and only moderatedeveloped or dry strength, and which possesses a high degree ofporosity; and, as well, to provide a method of producing foundrycompositions of the general type just described and possessing thegeneral qualities just hereinbefore recited.

Keeping in mind that western bentonite is ordinarily employed in orderthat advantage might be taken of its well-known colloidal swellingqualities upon ,the presence of added water, giving increased dry ordeveloped strength, it will appear that with the bentonite apparentlylosing its separate identity under microscopic study due to theencapsulation of the particles in the pitch or hydrocarbon, it wouldthereupon lose its swelling properties when water is added to mix ofwhich it constitutes an ingredient. My studies have disclosed, however,that such is not the case; but that, on the contrary, due to somephysical phenomenon as yet not fully understood by me, the normalswelling qualities of the bentonite are nevertheless displayed upon theaddition of water, despite such encapsulation. In brief, I achieve uponthe practice of my new mode of procedure, highly satisfactory resultsnot heretofore appreciated nor believed to be possible. Such new processis attended by the use of a radically diminished mulling time-aphenomenon of great practical advantage in foundry practice coupled witha simplification of the manipulative steps, the use of simplified andinexpensive equipment, and a demand for labor of but moderate skill.

During the course of my investigations, and under microscopic study ofsands coated with that plastic carbon or hydrocarbon known under thetrade name of Vanadiset, concerning the use of which more will be saidat a later point herein, and bonded with bentonite, and thereafterreacted with a solvent applied to the coating to enhance the chemicalbonding action thereof, I discovered that upon shaking the sand out ofthe flask, sifting and preparing the same for reuse, the bentonitecompletely disappeared from the slide plate of the microscope asobserved through the viewing aperture of the latter. At the same time,the bonding action of the bentonite persisted, substantially unabated.It was upon a consideration of the practical significance of thisphenomenon that my present invention is predicated.

In research predicated upon my observations, therefore, I prepared amechanical mix of a suitable non-thermal setting hydrocarbon, preferablya resin, and in the particular instance undergoing illustration, thatknown as Vanadiset, together with western bentonite.

Vanadiset is a non-thermal setting petroleum pitch which issubstantially free of products that are volatile below about 550 F. Itis black in the mass, fractures conchoidally and gives a brown streak onporcelain. The specific gravity at 77 F. is about 1.12 and the molecularweight about 3200. It softens at F. to 340 F. and is soluble in carbondisulphide, benzene and other aromatic solvents. Vanadiset essentiallyconsists of asphaltenes 20% to 70%, asphaltic resins 5% to 15%, and oilyconstituents 26% to 51%, with carbenes not over about 1%. Chemicalanalysis reveals that it contains about 21% to 64% unsaturatedhydrocarbons, with the fixed carbon content amounting to about 36% to18% and the hydrogen content about 9% or less. The ash content is lessthan 15% of which vanadium is the principal constituent.- (See, UnitedStates Patent 2,409,437 and the Bulletin of October 1,

1947, of the Wilson Carbon Company, Inc., 60

East 42d Street, New York 17, New York.)

In making my mix I used substantially equal parts of each material,Vanadiset" and western bentonite. These were mixed for a relativelyshort time until an intimate admixture was obtained. No furthertreatment of this mix was involved at that stage in the process. Iadmixed the mechanical mixture thus obtained with unbonded sand,preferably comprising subangular particles; and thereupon heated theresulting product to a temperature of approximately 500 F. and mulledthe same intimately for a short period oftime.

Examination of the resulting product disclosed that there was produced asand which was coated with a smooth layer, which layer was comprised ofa mixture of bentonite and petroleum resin. Microscopic study disclosedthat no particles of bentonite were visible. This justified acceptanceof the theory that the bentonite was insulated by a coating of pitchfrom contact with water.

As has been suggested hereinbefore, it would appear that by consequence,the addition of water would not be attended by swelling of the bentoniteor increase of either its bonding action or of the dry strength of thesand attendant upon its use. Quite on the contrary, however, I havefound that, upon activating the hydrocarbon by the addition of a liquidcontaining the three ingredients, Vanadiset," an aromatic solvent forthe pitch, and additional water, the coating comprising a mixture ofbentonite and petroleum pitch exhibited the qualities of a high degreeof bonding action, a high green strength, and requisite developed or drystrength. Perhaps the addition of the aromatic solvent momentarilysweeps aside the hydrocarbon capsule and exposes the otherwiseencapsulated bentonite to the action of the added water. I do not,however, desire to be bound by such explanation. Regardless of the exactreason why, my experiments amply bear out the conclusion that highbonding action and requisite green and dry strength are achieved, andthat castings produced from molds formed of such sands display finishdetails as good or better than those produced from molds formed ofcoated sand mixed with bentonite and water to which was added aliquid-containing solvent and resin, that is to say, sands evolved ingeneral according to the practice exemplified in the prior practicereferred to.

The overlying advantage of my new procedure as contrasted with the knownprior techniques, is the great saving in time and in the requirement ofbut a minimum of labor, and this relatively unskilled. Provided that thenew procedure approximates the known techniques in satisfactory results,it is apparent that my new procedure not only involves the recognitionof a new principles of operation, but incorporates many practicaladvantages.

In the practice according to my new technique, the bentonite isapparently protected from contact with water because of the pitchcoating. Nevertheless, a highly satisfactory bonding action takes placebetween the bentonite and the sand, particularly upon the addition ofthe activating liquid.

Moreover, it is to be noted that while in the mulling or mixing of thebentonite-petroleum mixture with the sand, the bentonite was raised to atemperature at which its advantageous properties would normally bedestroyed, nevertheless its bonding qualities apparently are in no wiseimpaired, while the thorough physical separation of the bentonite fromthe sand is ensured and the time of the process diminished. Moreover,although the Vanadiset and the bentonite are thoroughly intermixed,causing a. thick, impure layer of resin about the particles of sand,rather than a thin, pure protective coating such as is employed in theprior processes, yet my observations have been uniformly to the effectthat the subsequent chemical activation of the treated sand by theaddition of a petroleum base remains substantially unchanged, whenviewed from a commercial standpoint.

.Despite the presence of the thick, impure layer of resin, rather than athin, pure coating thereof. I have observed that the surface of thecasting produced in molds formed of my new treated sand are better thanusual. This indicates that no fusion to the surface of the cast metaloccurs, even when iron and steels are employed, involving high pouringtemperatures, either of the silica sand or of the bentonite. Apparently,therefore, it appears that my new procedure provides protection of thebentonite fromthe usual action of heat thereon, while at the same timeit does not interfere with the bonding action thereof. As statedhereinbefore, however, I am unable to explain the exact nature of thebonding action of the bentonite in the practice according to myinvention. I observe no wedge action of the bentonite; that is, nosubstantial tendency for the bentonite to concentrate at the anglesformed between two sand grains. Neither is there a continuous layer ofeither bentonite or bentonite and water.

Hereinbefore, I have referred to the use of Vanadiset. It is, of course,possible to employ in the stead thereof any suitable non-thermal settinghydrocarbon. This carbonaceous material resists burning on or stickingof the sand or clay to the poured metal by insuring that a predominantlyreducing atmosphere exists at and shortly after the time of pouring thecasting from the molten metal. It should persist sufficiently long topermit the poured metal to solidify. Moreover, such materials shouldimpart no substantial impairment to the flow and lay of the moltenmetal. It should offer little impairment to the green strength of thesand and should provide no appreciable increase in the dry or developedstrength thereof. Porosity should remain substantially unimpaired, sothat all gases and vapors flashed during the pouring operation may bequickly vented to the exterior without appreciable likelihood of damageeither to the mold or to the casting. To satisfy the foregoingrequirements, I find that the resin may be any suitable heavyhydrocarbon residue which is non-thermal setting in nature.

I desire that the hydrocarbon be non-thermal setting, so that the sandmay be shaken out of the flask, and after the addition of a small amountof additional binder and carbonaceous material, be subjected toreuse inthe preparation of additional molds. Typical of suitable petroleumproducts may be listed asphalts, asphaltites, hydrocarbons, carbonaceousmaterials, and the like. Vanadiset," which is a high-carbon,low-hydrogen, hydrocarbon produced from Venezuela crude oil, I findparticularly satisfactory for my purpose. Its high carbon content,together with low hydrogen especially suits it for resisting scaling ofthe casting and burning on of the sandor clay.

The practice of my invention results inappreciable reduction of themulling or mixing time when the sand is being used for the first time.As compared to an ordinary seven-minute mulling time, my new techniquesaves more than five minutes, or more than '70 Important time savings ofthis type are vital to successful foundry practice. Greater uniformityof the product is obtained since the bentonite and resin particlesaccording to one practice of my invention are distributed before beingworked into the sand. Minimum quantities of clay and hydrocarbon aretherefore employed with resultant advantages in diminished working time,diminished labor costs, decreased costs of materials, increasedporosity, diminished efiect on green and developed strength andincreased ease of shaking out of the flask ,following pouring. Theinitial mulling cycle is simplified, since the only additive need bewater, or water together with a suitable solvent.

Foundry compositions produced according to the practice of my inventiondisplay appreciable green strength with required moderate retainedstrength. Their ready flow and tamping qualities permit them to takesharp impressions, while the cohesion between the particles of thecomposition contribute towards resistance of marginal crumbling of thepattern. The carbonaceous coating resists the penertation of the moltenmetal into the body of the mold. Improved casting appearance results,due in part perhaps to the reducing atmosphere towards which thismaterial contributes, in the region of and at the time of pouring themolten metal. Burning on and sticking of the sand and clay particles tothe surface of the casting is prevented. I am able to produce cleanerand sharper castings, free from surface scale and other defects, so thatbut a minimum of subsequent grinding and pickling is required tocondition them for use.

In connection with the foregoing, a further advantage from amanufacturing standpoint attends upon the practice of my invention. Thisconcerns the brittleness of the hydrocarbon coating under conditions ofrapid cooling. Should the pitch, asphalt, or petroleum hydrocarbon befirst mixed with the sand and then heated, giving a smooth coating ofthe sand particles, nevertheless it is observed that when this materialis rapidly mulled, in an attempt to increase unit production, particlesof the coating will fiake oil. This is most undesirable, resulting insticking of the sand particles to the casting, and in the production ofa casting with rough surface detail. Should, however, the mixture ofbentonite, together with resin or hydrocarbon, be used in the sameprocess accordingto the practice of my invention, high production ismade possible with minimized likelihood of spalling and in thesubstantial absence of defective castings or rejects. Perhaps in my newtechnique the bentonite serves as a cushion.

Further refinement attendant upon the practice of my invention is theincreased cleanliness and control of the coating which for the firsttime is made possible. In this connection, it is to be noted'that groundand crushed petroleum resins such as Vanadiset are quite dusty. Adefinite, yet uncontrollable loss occurs when a mixture of resin andsand is placed in a dryer or heater. Not only is this undesirable, dueboth to the unpleasant natute of the dust particles, the hazard createdthereby and the loss of material, but as well, there is possibility oi'the production of a non-uniform product. When, however, ahentonite-resin mixture is added to the sand, particularly in thepresence of a small quantity of water, the dust loss is renderedinappreciable and a more uniform product results, possessing superiorqualities.

In accordance with the practice of my invention, the quantity of addedclay and carbonaceous material is insuflicient to affect detrimentallythe porosity of the mold or to bring about increase of the dry strength01' the latter. Since the same mixture or similar mixture of bentoniteand resin'may be used to maintain the sand during the course of its useand reuse in the foundry, it is to be observed that the used foundrycomposition is susceptible of ready recovery and reuse with but littleloss of material. Such reconditioning can be achieved with but minimumadditives of carbonaceous ingredients and minimum reworking.Accordingly, a substantial quantity of petroleum and bentonite coatingremaining on the sand, it follows that upon the admixture of but a smalladditional quantity of resin-bentonite mixture thereto, the used andscreened sands are thoroughly conditioned for reuse. Thus, I admix aboutto three per cent by weight of the 50-50 bentonite-Vanadiset mix to theused sand, intimately admixing the same therewith and therebyconditioning it for reuse.

It is to be noted that since the heavy petroleum residue which I employis non-thermal setting in nature, it does not case-harden in operation.Hence, the sand particles retain their desirable properties upon reuse.

The method is extremely rapid, and treated sands are prepared readilyand in'simple manner with but minimum requirement of time and use ofmaterials, and with the use of labor of but moderate skill. Theadmixture of the coating material with the sand is carried out in simplemanner, while reclaiming and reconditioning is readily accomplished. Allthese and many other highly practical and advantageous results attendupon the practice of my invention.

While in accordance with the practice of my invention, as illustrativelydescribed above, the bond clay and resin are first mixed together in drystate, heated at 500 F. and then intimately mixed with silica sand bymulling. I find that satisfactory results are had by heating and mullingconcurrently. This I achieve by dumping hot sand into the muller andaccomplishing the mixing with the mixed binder before the temperature ofthe whole drops below about 350 F. Excellent results also are achievedwhere the muller itself is heated, as by a special heating chamber builtaround the shell of the muller, and the sand consequently heated bycontact with the hot shell during the mulling operation.

Also, I find that certain benefits are achieved by mixing the bondingmix of clay and resin with silica sand in a rotary dryer. Thecombination of time and temperature in the dryer (sufficient to heat thecomposition to 500 F. or more) is such as to give a reasonablysatisfactory coating of the sand particles. Although the results had arenot as good as those achieved in accordance with the preferredembodimentof my invention, the manner of treatment is not as expensive either. Formany classes of work, therefore, the alternative method is entirelyadequate.

It is apparent from the foregoing that many modes of realization of myinventive concept will readily suggest themselves to those skilled inthe art, once the present procedure is disclosed. Similarly, it will beapparent that many modifications of the present embodiment will likewisesuggest themselves, all falling within the scope of my invention.Accordingly, I intend the foregoing disclosure simply as illustrative,and not by way of limitation.

I claim as my invention:

1. The method of producing treated foundry sands, comprising intimatelyand mechanically admixing about equal parts by weight of dry powderedwestern bentonite and dry powdered Vanadiset and heating the mixture andsimultaneously mixing with silica sand particles at such temperaturethat the composition is maintained at approximately 500 F. for asuflicient time to encapsulate the bentonite particles in Vanadiset andto 'form a fused coating of the encapsulated bentonite on the particlesof sand.

2. The method of producing treated foundry sands, comprising intimatelyand mechanically admixing about equal parts by weight of dry powderedwestern bentonite and dry powdered Vanadiset at a temperature of about500 F. and mulling the mixture together with hot silica sand attemperatures of approximately 500 F. for the whole composition for aperiod slightly less than two minutes.

3. The method of producing activated foundry sands, comprisingintimately and mechanically admixing approximately equal parts by weightof dry powdered western bentonite and dry powdered Vanadiset and mullingthe same with silica sand particles at elevated temperatures such thatthe composition is maintained at a temperature of 500 F., and thereafteractivating the mix thus obtained through the addition of a liquidcontaining an aromatic solvent and water.

' crete sand particles with the encapsulated ben- 4. Treated foundrysand consisting essentially of discrete-silica sand particles, with athermally fused coating thereon initially consisting of powdered westernbentonite and powdered Vanadiset admixed in about equal parts by weight,the bentonite being thoroughly encapsulated in the Vanadiset, and themixture of bentonite and Vanadiset forming the thermally fused coatingon the particles of sand.

5. Activated foundry sand consisting essentially of discrete silica sandparticles having a thermally fused coating thereon consisting of amechanical mixture of about equal parts by weight of powdered westernbentonite and powdered Vanadiset and wetted by liquid contain ing anaromatic solvent, water and additional Vanadiset.

6. The method of reconditioning a foundry sand system, comprisingmechanically mixing dry powdered western bentonite and dry powderedVanadiset at a temperature of about 500 F. and mixing the same with usedsilica sand particles at such temperature and for such period of time toencapsulate bentonite in Vanadiset and to achieve a desired fusedcoating of distonite and Vanadiset. KENNETH RAY GRUBE.

REFERENCES CITED Z The following references are of record lin the fileof this patent:

UNITED STATES PATENTS Number Name Date 2,159,952 Jones May 23, 19392,162,059 Chedic June 13, 1939 2,256,832 King Sept. 23, 1941 2,409,437La Cross Oct. 15, 1946 2,432,702 Wallace Dec. 16, 1947 2,444,413 WestonJuly 6, 1948

3. THE METHOD OF PRODUCING ACTIVATED FOUNDRY SANDS, COMPRISINGINTIMATELY AND MECHANICALLY ADMIXING APPROXIMATELY EQUAL PARTS BY WEIGHTOF DRY POWDERED WESTERN BENTONITE AND DRY POWDERED VANADISET AND MULLINGTHE SAME WITH SILICA SAND PARTICLES AT ELEVATED TEMPERATURES SUCH THATTHE COMPOSITION IS MAINTAINED AT A TEMPERATURE OF 500*F., AND THEREAFTERACTIVATING THE MIX THUS OBTAINED THROUGH THE ADDITION OF A LIQUIDCONTAINING AN AROMATIC SOLVENT AND WATER.
 4. TREATED FOUNDRY SANDCONSISTING ESSENTIALLY OF DISCRETE-SILICA SAND PARTICLES, WITH ATHERMALLY FUSED COATING THEREON INITIALLY CONSISTING OF POWDERED WESTERNBENTONITE AND POWDERED VANADISET ADMIXED IN ABOUT EQUAL PARTS BY WEIGHT,THE BENTONITE BEING THOROUGHLY ENCAPSULATED IN THE VANADISET, AND THEMIXTURE OF BENTONITE AND VANADISET FORMING THE THERMALLY FUSED COATINGON THE PARTICLES OF SAND.